let a = ()=>{
    return new Promise((resolve,reject)=>{
        setTimeout(()=>resolve('hello'),10)
    })
};
let b = ()=>{
    return new Promise((resolve,reject)=>{
        setTimeout(()=>resolve('lagou'),10)
    })
};
let c = ()=>{
    return new Promise((resolve,reject)=>{
        setTimeout(()=>resolve('I love you'),10)
    })
};
console.log('start');
Promise.all([a(),b(),c()]).then(value =>{
    let result ='';
    for (let item of value){
        result+=item+' ';
    }
    console.log(result);
});
console.log('next');
//执行结果
// start ,netxt , hello lagou I love you 